The primary purpose of roadway lighting is to provide for quick, accurate and comfortable vision at night to make streets and highways useful during the night as well as during the day. Proper and adequate lighting can thus reduce nighttime accidents, aid police protection, facilitate traffic flow and promote business, industry and community well-being in the area. These objectives are described in the publication entitled "American National Standard Practice for Roadway Lighting", published by the Illuminating Engineering Society of North America (1983). It includes the illumination standards known as ANSI/IES RP-8, commonly referred to simply as "RP-8".
In order to achieve these desirable objectives and to be consistent with economic realities and manufacturing capabilities, the luminaires used for roadway lighting should meet the criteria established by RP-8 and the manufacturers of such luminaires must also keep the manufacturing cost to a minimum so that the communities involved can make best use of such lighting facilities. The criteria set forth in RP-8 take into account such factors as the nature of abutting land use, the reflective characteristics of the roadway surface and the kinds of traffic to be expected on the roadway itself. It would be pointless to reiterate the content of the above document herein, and the document is therefore incorporated by reference for all purposes. It should be sufficient, however, to say that uniform lighting of the surface with adequate luminance and maximum spacing between support poles, consistent with the standards of RP-8, is the objective of luminaire design.
Examples of prior art luminaires can be found in the following U.S. patents.
U.S. Pat. No. 3,257,553, Tolbert PA1 U.S. Pat. No. 3,251,987, Wince PA1 U.S. Pat. No. 3,184,199, Clark PA1 U.S. Pat. No. 2,913,570, Gough PA1 U.S. Pat. No. 4,341,018, Fratty PA1 U.S. Pat. No. 1,199,071, Heckert PA1 U.S. Pat. No. 1,471,166, Jones PA1 U.S. Pat. No. 1,903,417, Grant PA1 U.S. Pat. No. 3,740,545, Franklin PA1 U.S. Pat. No. 3,700,883, Donohue PA1 U.S. Pat. No. 4,237,528, Baldwin PA1 U.S. Pat. No. 4,242,727, deVos PA1 U.S. Pat. No. 4,081,667, Lewin PA1 U.S. Pat. No. 4,028,542, McReynolds, Jr.
It will be observed that the illuminating devices in these patents include reflectors and refractors for various purposes in addition to roadway illumination. They are included to demonstrate that a variety of techniques have been employed to obtain certain illumination distribution patterns including the technique of forming facets on the interior of a reflector as well as using optical refractors to cooperate with a reflector to achieve the desired distribution. However, these reflectors have various shortcomings and are not able to accomplish the desired result.